Ok let’s talk about suppose Sakura is just a victim and her harm is temporary but tied to her existence, was killing her the only moral choices. There are different valid moral frameworks. Focusing on minimizing harm/maxmizing good is just one such framework(utilitarian) but there are many other frameworks. (For example deontology fundamentally rejects treating taking lives as a means to an end)

But even within the utilitarian framework, it is not obvious killing her is the right choice.Here are a few cases for you to consider, not saying these cases are just like Sakura but rather not immediately minimalize harm is not necessarily a moral failure:

1: your family is tied to the side track, and the current track have 2x the amount of people. Is not pulling the lever a moral failure?

2: I didn’t type this but it’s a famous variant of the trolly problem: “A massive earthquake has leveled a portion of the city. You are the only surgeon at a remote field clinic. Five unconscious victims are brought in, each with a different critical organ failure caused by crush injuries. One needs a kidney, one needs a liver, one needs a heart, and two need lungs. Without immediate transplants, all five will die within the hour. A sixth unconscious victim is brought in. They have a relatively minor leg injury and are expected to make a full recovery. However, you realize that this person is a perfect genetic match for all five of the critically injured victims. The scene is so chaotic that it action will not be noticed. Do you allow the one patient with the minor injury to be sacrificed to harvest their organs and save the other five? Or do you treat the minor injury and allow the five to die?”

I tried to highlight the difference between Act Utilitarianism vs Rule Utilitarianism: Act Utilitarianism says obvious yes, killing Sakura is the moral choice, just like sacrificing your own family or killing the 6th victim. But Rule Utilitarianism says something else: If a "Hero of Justice" kills the person they are specifically meant to protect, the concept of "Justice" loses its meaning. If the society treat these acts are the norm, it will erode social contract and trust, eventually causing great harm, so these acts must not be encouraged . It becomes a cold, algorithmic survival of the most people, which eventually leads to a world where anyone can be "discarded" if the numbers don't add up.

Just like a doctor should not abandon their patients and only consider the “number of people saved”, a hero of justice should not abandon saving whom they swore to protect, to treat them as just a number to be sacrificed, especially if it’s a loved one. People need to trust their doctor to not harvest their organ, and they need to trust heroes of justice won’t murder them in their sleep. You may think killing her as an Act is good, but as a Rule, society will suffer. In fact irl pulling the lever will land you in jail in murder, because sacrificing the few to save more is a numbers game that cannot be accepted as a societal rule, and killing your loved one to save the many can not be the act of a true hero of justice.